This invention relates to an acrylic resin-containing metal surface treatment composition, treatment method and treated metal material, and in particular to an acrylic resin-containing metal surface treatment composition, treatment method and treated metal material giving improved corrosion resistance, film adhesion and slip properties (referred to also as xe2x80x9clubricityxe2x80x9d).
Conventionally, phosphate treatment, chromate treatment and non-chromate treatment, etc. were performed as surface treatments for food cans, car bodies, coil coatings for steel plate and metals for construction materials. For example, a phosphate film is formed on a metal surface as a pretreatment when organic coatings such as paints and adhesives are applied to metal surfaces such as iron, zinc, and aluminum. By subsequently applying an organic film such as a coating, corrosion resistance and film adhesion can be improved. However, conventional phosphate treatment did not necessarily provide sufficient corrosion resistance, film adhesion or slip properties to satisfy demand in recent years.
To improve corrosion resistance following phosphate treatment, it was common to apply a coating after first applying a primer coat. However, if a primer was first applied, although corrosion resistance and film adhesion improved, the number of coating steps increased, complicating the procedure and leading to higher cost.
xe2x80x9cA Metal Surface Treatment for Composite Filmsxe2x80x9d of Japanese Patent Laid-open publication No. Hei 5-117869 was proposed for example as a metal surface treatment which aims to omit the primer coating while giving highly developed corrosion resistance and film adhesion. The metal surface treatment of the aforesaid Japanese Patent Laid-open publication No. Hei 5-117869 is a phosphate surface treatment liquid comprising a cationic organic polymer compound or one of its salts having one or more cationic nitrogen atoms, and a molecular weight in the range of 1,000-1,000,000.
In the xe2x80x9cSurface Treatment Method for Aluminum and Aluminum Alloysxe2x80x9d described in Japanese Laid-open publication No. Sho 51-73938, the metal to be treated is limited to aluminum. This method aims to confer corrosion resistance and film adhesion properties. It is described that this metal surface treatment method uses a liquid of which the principal components are water-soluble resins such as vinyl acetate, vinylidene chloride and acrylic acid or organic polymer film forming substances comprising emulsion resins, and a water-soluble titanium compound.
However, although they offer improved corrosion resistance and film adhesion compared with the prior art, neither the aforesaid metal surface treatment agent nor treatment method has reached recent demand requirements. In particular, in the manufacture of food cans using aluminum or its alloys, they do not prevent jamming, and in the coil coating of steel plate, lubricity is poor.
It is therefore an object of this invention to provide an acrylic resin-containing metal surface treatment composition, treatment method and treated metal material offering improved corrosion resistance, film adhesion and slip properties.
To achieve this object, the acrylic resin-containing metal surface treatment composition according to this invention comprise:
a) a water-soluble, water-dispersible or emulsifiable acrylic resin comprising either an amino group or an ammonium group, or both, together with a hydroxyl group and hydrophobic group, and
b) a heavy metal or one of its salts.
As permeability is suppressed by an inorganic film which comprises a heavy metal or one of its salts, corrosion resistance improves. Further, as the amino group or ammonium group in the acrylic resin is coordinated with the (heavy) metal, the aforesaid inorganic film is connected via the acrylic resin. This prevents cohesive failure of the inorganic film, giving an almost uniform substrate film on the metal surface which improves adhesion between the substrate film and the topcoat. The substrate film of this invention refers to the film formed on the metal surface which comprises the aforesaid inorganic film connected by the acrylic resin. In addition, the aforesaid acrylic resin is almost uniformly distributed on the substrate film surface, so frictional resistance is reduced and slip properties are improved.
Preferably, the amino group or the ammonium group in the acrylic resin-containing metal surface treatment composition according to this invention comprises at least the structural unit represented by the following chemical formulae (I) or (II). 
where R1, R2 are hydrogen, hydroxyl, a substituted or unsubstituted straight chain or branched alkyl group comprising 1-5 carbon atoms, or a substituted or unsubstituted straight chain or branched hydroxyalkyl group comprising 1-5 carbon atoms 
where R3, R4, R5 are hydrogen, hydroxyl, a substituted or unsubstituted straight chain or branched alkyl group comprising 1-5 carbon atoms, or a substituted or unsubstituted straight chain or branched hydroxyalkyl group comprising 1-5 carbon atoms.
Moreover, the molecular weight of the acrylic resin in this invention is 500-100,000, and preferably 1,000-20,000. When the molecular weight is less than 500, corrosion resistance decreases. On the other hand, when the molecular weight exceeds 100,000, hydrophilic properties decrease.
According to this invention, the acrylic resin content is 0.01-10 g/l and preferably 0.1-5 g/l relative to the metal surface treatment composition. When the acrylic resin content is less than 0.1 g/l, a binder effect is not manifested, and the physical durability of the substrate film decreases. On the other hand, when the acrylic resin content exceeds 10 g/l, the adhesion between the substrate film and the metal surface decreases.
In the acrylic resin-containing metal surface treatment composition according to this invention, the acrylic resin contains 1-10 amino and/or ammonium groups, 1-10 hydroxyl groups and 1-5 hydrophobic groups per 1000 molecular weight units of acrylic resin. When there is less than one amino or ammonium group per 1000 molecular weight units of acrylic resin, hydrophilic properties and adhesion to the metal decrease. On the other hand, when there are more than 10 amino or ammonium groups per 1000 molecular weight units of acrylic resin, corrosion resistance decreases.
When there is less than one hydroxyl group per 1000 molecular weight units of acrylic resin, hydrophilic properties and film adhesion decrease. On the other hand, when there are more than 10 hydroxyl groups per 1000 molecular weight units of acrylic resin, corrosion resistance decreases.
When there is less than one hydrophobic group per 1000 molecular weight units of acrylic resin, corrosion resistance and slip properties decrease. On the other hand, when there are more than 5 hydrophobic groups per 1000 molecular weight units of acrylic resin, hydrophilic properties and film adhesion decrease.
In the acrylic resin-containing metal surface treatment composition, the amino group or ammonium group contained in the acrylic resin is introduced by copolymerization of a monomer comprising at least the structural unit represented by the following chemical formulae (III) or (IV): 
where R6 is hydrogen or methyl, R7, R8 are hydrogen, hydroxyl, a substituted or unsubstituted straight chain or branched alkyl group comprising 1-5 carbon atoms, or a substituted or unsubstituted straight chain or branched hydroxyalkyl group comprising 1-5 carbon atoms, and R9 is an alkylene group comprising 1-5 carbon atoms. 
where R10 are hydrogen or methyl, R11, R12 are hydrogen, hydroxyl, a substituted or unsubstituted straight chain or branched alkyl group comprising 1-5 carbon atoms, or a substituted or unsubstituted straight chain or branched hydroxyalkyl group comprising 1-5 carbon atoms, and R13 is an alkylene group comprising 1-5 carbon atoms.
In the acrylic resin-containing metal surface treatment composition according to this invention, the hydroxyl group contained in the acrylic resin is introduced by copolymerization of a monomer comprising at least the structural unit represented by the following chemical formula (V): 
where R14 is an alkylene group comprising 1-4 carbon atoms, and R15 is hydrogen or methyl.
Moreover, in the acrylic resin-containing metal surface treatment composition according to this invention, the hydrophobic group contained in the acrylic resin is introduced by copolymerization of a monomer comprising at least the structural unit represented by the following chemical formula (VI): 
where R16 is a straight chain, branched or cyclic alkyl group comprising 4-18 carbon atoms, and R17 is hydrogen or methyl.
In the acrylic resin of the acrylic resin-containing metal surface treatment composition of this invention, copolymers of the following monomers are suitable.
(1) The acrylic monomer containing an amino group (ammonium group) may for example be N,N-dimethylaminoethyl(meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, (meth)acrylamide, N,N-dimethylacrylamide, N-methylolacrylamide, N-methylaminopropyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, N-ethylamino propyl(meth)acrylamide, N,N-diethylaminopropyl (meth)acrylamide, or chlorides of these compounds.
(2) The acrylic monomer containing a hydroxyl group may for example be 2-hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, 4-hydroxybutyl (meth)acrylate, or 2,3-dihydroxypropyl(meth)acrylate.
(3) The monomer containing a hydrophobic group may for example be n-butyl(meth)acrylate, i-butyl (meth)acrylate, t-butyl(meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl(meth)acrylate, lauryl (meth)acrylate, stearyl(meth)acrylate, cyclohexyl (meth)acrylate, isobornyl(meth)acrylate, styrene, p-t-butylstyrene, vinyltoluene, vinylphenol or benzyl (meth)acrylate.
(4) Additionally, other monomers may be added such as acrylic acid, methacrylic acid, maleic acid, itaconic acid or acrylonitrile.
The copolymerization ratios of copolymers formed from the aforesaid monomers are amino group (ammonium group)-containing acrylic monomer 5-60 weight %, hydroxyl group-containing acrylic monomer 20-80 weight %, hydrophobic group-containing monomer 5-50 weight %, and other monomers 0-30 weight %. More preferably, these ratios are amino group (ammonium group)-containing acrylic monomer 20-40 weight %, hydroxyl group-containing acrylic monomer 30-60 weight % and hydrophobic group-containing monomer 20-40 weight %.
When the copolymerization ratio of the amino group (ammonium group)-containing acrylic monomer in the aforesaid copolymer is less than 5 weight %, hydrophilic properties decrease, and the connectivity of the acrylic resin and inorganic film comprising the heavy metal or salt decreases. On the other hand, when the copolymerization ratio of the amino group (ammonium group)-containing acrylic monomer in the aforesaid copolymer exceeds 60 weight %, corrosion resistance decreases.
When the copolymerization ratio of the hydroxyl group-containing acrylic monomer in the aforesaid copolymer is less than 20 weight %, hydrophilic properties and film adhesion decrease. On the other hand, when the copolymerization ratio of the hydroxyl-group-containing acrylic monomer in the aforesaid copolymer exceeds 80 weight %, corrosion resistance decreases.
When the copolymerization ratio of the hydrophobic group-containing monomer in the aforesaid copolymer is less than 5 weight %, slip properties and corrosion resistance decrease. On the other hand, when the copolymerization ratio of the hydrophobic group-containing monomer in the aforesaid copolymer exceeds 50 weight %, hydrophilic properties and film adhesion decrease.
Heavy Metals
In the acrylic resin-containing metal surface treatment composition according to this invention, the heavy metal is at least one of the metals zirconium (Zr), molybdenum (Mo), tungsten (W), niobium (Nb), nickel (Ni), cobalt (Co), manganese (Mn) and tantalum (Ta).
The source of the aforesaid heavy metal is preferably a complex fluoride of the heavy metal, other examples being a nitrate or phosphate.
The content of the complex fluoride of the heavy metal is preferably 0.01-10 g/l relative to the acrylic resin-containing metal surface treatment composition of this invention. When the content of the complex fluoride of the heavy metal is less than 0.01-10 g/l corrosion resistance decreases. On the other hand, when the content of the complex fluoride of the heavy metal exceeds 10 g/l, corrosion resistance again decreases.
The acrylic resin-containing metal surface treatment composition according to this invention may also contain a phosphoric acid or phosphate.
Examples of the phosphoric acid or phosphate are H3PO4, Na3PO4, Na2HPO4, NaH2PO4 and (NH4)3PO4.
The content of the phosphoric acid or phosphate is 0.01-20 g/l, but preferably 0.05-0.1 g/l, relative to the aforesaid acrylic resin-containing metal surface treatment composition. When the phosphoric acid or phosphate content is less than 0.01 g/l, corrosion resistance decreases. When the phosphoric acid or phosphate content exceeds 20 g/l, film adhesion decreases.
The acrylic resin-containing metal surface treatment composition according to this invention may also contain the following etchants and etching assistants optionally.
Etchants
As etchant, hydrogen fluoride or one of its salts may be used. The etchant content may be 0.005-0.5 g/l relative to the metal surface treatment composition. When the etchant content is less than 0.005 g/l, etching is insufficient, and the substrate film is not sufficiently formed on the metal surface. On the other hand, when the etching content exceeds 0.5 g/l, etching is excessive.
Etching Assistants
As etching assistants, hydrogen peroxide (H2O2), nitrous acid (HNO2), HBF4 or one of its salts may be used. The etching assistant content may be 0.005-5 g/l of hydrogen peroxide (H2O2), nitrous acid (HNO2) or nitrous acid salt relative to the metal surface treatment composition. When this content is less than 0.005 g/l, corrosion resistance decreases. On the other hand, even if the content exceeds 5 g/l, corrosion resistance decreases. Moreover, it is preferable that the content of HBF4 or its salt is 0.003-0.2 g/l relative to the metal surface treatment composition. When this content is less than 0.003 g/l, corrosion resistance decreases. On the other hand, even if the content exceeds 0.2 g/l, corrosion resistance decreases.
Operating Conditions and Treatment Method
In the metal surface treatment method according to this invention, the aforesaid acrylic resin-containing metal surface treatment composition is brought in contact with a metal surface, and the surface is then rinsed in water and dried.
The pH of the aforesaid metal surface treatment composition is approximately 2.0-5.0, but preferably 2.5-3.5. The adjustment of pH is performed by NaOH, aqueous ammonia or nitric acid. The contact temperature of the metal surface treatment composition and metal material of this invention is normal temperature (e.g. 20xc2x0 C.)-90xc2x0 C., and preferably 35-65xc2x0 C. In general, the contact time of metal material and the acrylic resin-containing metal surface treatment composition according to this invention is shorter the higher the contact temperature.
When the composition of this invention is sprayed on the metal material, it is usual to make contact for approximately 5 seconds-5 minutes, but preferably for 10-60 seconds. When the dipping method is used, a longer contact time than the aforesaid contact time is required. Additionally, contact can be made by the flow coat method and the roll coat method.
The metal material to which the surface treatment is given as aforesaid is rinsed in water, and enters a drying step. The drying temperature is 150-240xc2x0 C., and at less than 150xc2x0 C., corrosion resistance decreases.
In the aforesaid rinsing step, after the metal material and the composition of this invention are brought in contact, the surface-treated metal material is rinsed with water to remove composition which did not become a a chemical conversion coating. According to this invention, an inorganic-organic chemical coating is obtained in a one step process.
The surface-treated metal material according to this invention is characterized by the fact that it is surface-treated using the aforesaid acrylic resin-containing metal surface treatment composition.